In the wrong hands, Shona Auerbach's Dear Frankie could have gone way off the sentimentality scale. Look at the elements: a single mother, a deaf child and a long-absent father about to enter the boy's life for the first time.

Add small-town pluckiness and the romantic draw of the sea and alarm bells begin to ring. Remaining on the right side of that perilous line is Auerbach's greatest accomplishment in a movie full of triumphs big and small.

Lizzie Morrison (Emily Mortimer) moves to a seaside Scottish town with her 9-year-old boy Frankie (Jack McElhone) and her mother, Nell (Mary Riggans). This is clearly not the first time the trio has been uprooted. The stress of adapting to new schoolmates and a change in environment doesn't faze the hearing-impaired boy, who has inherited healthy self-esteem and independence from his mother.

Another source of strength for Frankie is his father, a crewman who seems to be perpetually at sea, but who sends him adventure-filled letters. It's through the correspondence with his "da," which we hear through voice-overs, that we discover a little of Frankie's inner world: he rarely speaks and has a habit of not wearing his hearing aid.

The letters also keep Lizzie connected to her son. You see, there is no father at sea. Lizzie is the one picking up Frankie's letters at the post office and replying to them. To avoid telling Frankie the unsavoury truth about his abusive father - Frankie wasn't born deaf - she has created a sweet, gentle dad to replace the one he never had.

But oh, what a tangled web we weave. Suddenly, the HMS Accra, the ship Frankie's father is supposed to be on, is about to dock in the boy's home town. Lizzie has to ask a complete stranger (Gerard Butler) to play the role of Frankie's dad. To make matters more stressful, Frankie's real father is dying and asking to see his son.

If Dear Frankie had been made in the U.S., there's no telling how many contrived plot devices would have been forced into the script to tie everything up with a neat, happy bow at the end. Instead, Auerbach gives us life - with all its long, uncomfortable silences, moral ambiguities and unfulfilled dreams. Yet for all its honesty, the film will still evoke a joyful tear or two. Not bad for a feature directing debut.

The cast members make virtually no missteps. Mortimer, who brings heart-wrenching humanity to her portrayal of Lizzie, has a special chemistry with McElhone that the camera clearly loves. Butler, recently seen in The Phantom of the Opera, is magnetic as the stranger, while Riggans and Sharon Small, who plays Lizzie's friend Marie, find their rhythm early and never let go.

All this and the Scottish coast. Dear Frankie is one love letter we'll be able to look back on in 10 years without embarrassment.